The oligomerization of olefins such as isobutylene using a sulfonic acid-type ion exchange resin catalyst is well-known in the art. For instance, U.S. Pat. No. 4,100,220 describes isobutylene oligomerization using a sulfonic acid resin catalyst and tertiary butyl alcohol (TBA) selectivity enhancing modifier to produce diisobutylene (DIB). In addition, U.S. Pat. No. 4,447,668 discloses isobutylene oligomerization using sulfonic acid resin catalyst A-15 with methyl t-butyl ether as solvent. U.S. Pat. No. 5,877,372 describes the selective oligomerization of isobutylene using a sulfonic acid resin catalyst, TBA selectivity enhancing modifier and isooctane diluent. U.S. Pat. No. 6,376,731 further discloses the oligomerization of isobutylene in the presence of a C3-C4 alkane diluent to enhance oligomerization selectivity and TBA to promote selectivity to DIB.
The DIB product may be used as such or may be hydrogenated to isooctane as described in U.S. Pat. Nos. 5,877,372 and 6,376,731. DIB and isooctane are potential fuel blending compositions.
In the production of DIB, it is found that minimization of water is essential to reduce detrimental unit corrosion and catalyst deactivation. However, water is often fed to the reaction section as a reactant impurity. Water is also produced by the dehydration of co-fed TBA. Because isobutylene and/or TBA streams may be recycled back to the reaction section, water can accumulate within the process such that unwanted corrosion or catalyst deactivation may occur.
Previous processes have been taught to purify DIB product. However, none of these processes have effectively dealt with the detrimental effects of water. U.S. Pat. No. 6,863,778 teaches a process to separate DIB from TBA using two distillation columns. DIB is removed as bottoms from the first distillation column and unreacted C4's are removed as overheads. A side draw containing a DIB/TBA azeotrope is fed to the second distillation column and TBA is recovered as bottoms and recycled to the reactor. However, in processes using side draws, the inventors have found that water and TBA distribute between the overhead distillate and the side draw. Water is extremely difficult to remove from either stream since water and TBA are mutually soluble. Thus, the presence of at least 1 weight percent TBA in these streams makes water soluble enough that it cannot be removed with a simple decantation step.
U.S. Pat. No. 4,559,108 also teaches a two distillation column purification of a C4 hydrocarbon feed to produce a purified isobutylene stream and a high boiling component stream comprising tertiary butyl alcohol and diisobutylene. However, the TBA and DIB were not separated and there is no mention of water in the process.
In sum, new methods to produce diisobutylene by oligomerization of isobutylene over a sulfonic acid-type ion exchange resin catalyst are needed. Particularly needed are processes which limit the amount of water in the oligomerization reactor.